External-cavity Mode-locked Laser Research Articles

Orange-to-red tunable picosecond pulses by frequency doubling in a diode-pumped PPKTP waveguide

A compact picosecond all-room-temperature orange-to-red tunable laser source in the spectral region between 600 and 627 nm is demonstrated. The tunable radiation is obtained by second-harmonic generation in a periodically poled potassium titanyl phosphate (PPKTP) multimode waveguide using a tunable quantum-dot external-cavity mode-locked laser. The maximum second-harmonic output peak power of 3.91 mW at 613 nm is achieved for 85.94 mW of launched pump peak power at 1226 nm, resulting in conversion efficiency of 4.55%.

High peak-power picosecond pulse generation at 126 µm using a quantum-dot-based external-cavity mode-locked laser and tapered optical amplifier

In this paper, we present the generation of high peak-power picosecond optical pulses in the 1.26 μm spectral band from a repetition-rate-tunable quantum-dot external-cavity passively mode-locked laser (QD-ECMLL), amplified by a tapered quantum-dot semiconductor optical amplifier (QD-SOA). The laser emission wavelength was controlled through a chirped volume Bragg grating which was used as an external cavity output coupler. An average power of 208.2 mW, pulse energy of 321 pJ, and peak power of 30.3 W were achieved. Preliminary nonlinear imaging investigations indicate that this system is promising as a high peak-power pulsed light source for nonlinear bio-imaging applications across the 1.0 μm - 1.3 μm spectral range.

High power all-quantum-dot-based external cavity modelocked laser

An all-quantirm-dot based external cavity modelocked laser using a quantum-dot gain medium and SESAM is demonstrated for the first time. This laser produces average powers of up to 27 mW and modelocking has been obtained over a range of cavity repetition frequencies from 350 MHz to 1.5 GHz. Additional RF modulation has also been used to further improve the modelocked operation.

Semiconductor Laser as High Speed Functional Device.

Research trends of semiconductor lasers as high speed functional device are reviewed. Enhanced nonlinear-optical response in the active region of semiconductor laser offers excellent functionality such as femtosecond pulse source, optical switch and wavelength converter. Specifically the research efforts on broad bandwidth anti-reflection coating for semiconductor laser amplifiers and external cavity mode-locked lasers are summarized. Bandwidth of 100 nm with reflectivity of 10-4 is expected.

A mobile broad-band communication system based on mode-locked lasers

A concept is proposed for a pico-cellular network for broad-band mobile communication on a millimeter-wave basis. How microwave optical-signal-processing techniques based on mode-locked lasers (MLLs), optical modulators, and high-speed photo diodes (PD's) can advantageously be applied in the optical feeder lines of a pico-cellular network at 60 GHz is investigated. The external cavity MLL (at 81.25 GHz) used for the experiments showed a single-sideband (SSB) phase noise of -59 dBc/Hz at 100-Hz offset, when actively locked at 6.25 GHz. With the PD, and limited by the V-band mixer equipment, spectral harmonics up to 100 GHz could be detected. For the downlink configuration, a 400-MHz subcarrier is modulated with a 155-Mb/s data signal and upconverted to 62.9 GHz using an MLL and a fast PD. The upconverted sideband at 62.9 GHz was received with an optical power of -14.3-dBm at a bit-error-rate (BER) equal to 10/sup -9/ without any additional penalty due to transmitting the signal over 3 km of optical fiber. BER measurements at 155 Mb/s down to 10/sup -11/ were made. For the uplink, the digitally encoded RF signal is downconverted also by optical microwave signal processing. A 155-Mb/s data encoded 19.21-GHz signal is downconverted to 460 MHz using a mode-locked laser, an optical modulator, and a 600-MHz optical receiver front end. A receiver sensitivity of -24.5 dBm (BER equal to 10/sup -9/) is demonstrated with the microwave signal being transmitted over a 1-m radio link and 3 km of optical fiber.

The electro-optic applications of InP

The electro-optic applications of InP and GaInAsP are reviewed. For fiber optics applications, diode lasers have been developed with low cw room-temperature threshold currents (25 mA), high modulation frequencies (>2 GHz) and long cw room-temperature lifetimes (>10 4 h). Avalanche photodiodes which have the p-n junction avalanche region in InP and the photosensitive region in GaInAsP have been made with peak avalanche gains of several hundred and with very low leakage currents (0.2 nA) at a gain of ten. For signal-processing applications and possibly for communications applications, an external-cavity mode-locked laser has been operated with pulse widths of ∼18 ps, an integrated Q-switched laser modulator has been operated at 2.2 GHz, and InP optoelectronic switches with very fast (<50 ps) response times have been demonstrated.